The invention relates to a belt assembly, in particular for driving camshafts of an internal combustion engine, including a driving gear, at least one driven gear, a belt, as well as a first and a second tensioner blade. Both tensioner blades are connected together in a manner that transmits a defined force and/or motion.
The camshafts of internal combustion engines are typically driven, starting from the crankshaft, by means of a traction mechanism, such as a control chain or a control belt. In order to prevent vibrations, and in particular transverse vibrations, tensioners are used to tension the belt. Such an arrangement with a chain tensioner, which includes a shoe subjected to the action of mechanical force by way of a leaf spring is described in DE 4114948 A1.
In an arrangement described in DE 4114948 A1, as the tension increases in the strand assigned to the tensioner—for example, due to vibrations of the camshafts—, the other strand becomes slack at least for a short period of time, so that undesired transverse vibrations are excited in the belt. A remedy could be provided with a drive system as shown in DE 201 02 748U1. In this drive system, two tensioner blades are hinged swivellably on one side to a housing of a tensioning device; and hydraulic pistons, acting from inside against the tensioner blades, are mounted in the opposite direction of tension in the housing between the tensioner blades. Therefore, the pistons are supplied over a common hydraulic connection, so that the conditions for adjusting the tension characteristics are met. The drive system described in DE 201 02 748 U1 includes two tensioning devices, which, including the housing, the tensioning pistons and the tensioner blades, are constructed symmetrically in relation to a center line.
As a result of DE 201 02 748U1, the two swivellable tensioner blades are connected together in a manner that transmits a force and motion by way of the two coupled hydraulic pistons. However, there is neither a reference in relation to the stationary housing of the internal combustion engine nor is the transfer of vibrations of one tensioner blade, excited, for example, by oscillating camshafts, to the other tensioner blade, controllable. In addition, the symmetrical design of the tensioning device, which necessitates a linear vibration system, favors the build up of vibrations and, thus, the risk of damage or even the destruction of the belt assembly. Another problem may stem from the air bubbles in the hydraulic system of the pistons. These air bubbles lead to an unknown spring system between the tensioner blades.
There is therefore needed an aforementioned belt assembly, which enables a defined and controlled application of the tension force to the tensioner blades for the active prevention of undesired transverse vibrations. In addition, the belt assembly should be designed simply and optimally and, at the same time, be easy and advantageous to produce, maintain and repair.
These needs are met according to the invention by a belt assembly, in particular for driving camshafts of an internal combustion engine, including a driving gear, at least one driven gear, a belt as well as a first and a second tensioner blade, both tensioner blades being connected together in a manner that transmits a defined force and/or motion by way of a two-part hinge mechanism. One tensioner blade can be subjected to the action of tension force by a first tensioning device, supported on the tensioner blade on one side and externally on the other side. The two parts of the hinge mechanism are connected together in a hinge point. The hinge point can be subjected to the action of tension force by a second tensioning device, and the second tensioning device is supported at the hinge point on the one side and at least indirectly on the internal combustion engine side on the other side.
Thus, according to the underlying idea, one tensioner blade can be subjected to the action of tension force by use of a first tensioning device, supported on the tensioner blade on one side and externally on the other side; and the two parts of the hinge mechanism are connected together in a hinge point. The hinge point can be subjected to the action of tension force by use of a second tensioning device; and the second tensioning device is supported at the hinge point on the one side and at least indirectly on the internal combustion engine side on the other side.
As an alternative, the problem, underlying the invention, may be solved with a belt assembly wherein a tensioner blade can be subjected to the action of tension force by use of a first tensioning device, which is supported on the tensioner blade on one side and externally on the other side. The second tensioner blade includes a second tensioning device with a piston, guided in a cylinder, which is constructed integrally in the tensioner blade; and the connecting link is connected in an articulated manner to the first tensioner blade on one side and to the second tensioning device on the other side.
Another alternative solution of the problem, underlying the invention, may be carried out with a belt assembly wherein a tensioner blade can be subjected to the action of tension force by use of a first tensioning device, which is supported on the tensioner blade on one side and externally on the other side. The second tensioner blade includes a second tensioning device with a piston, guided in a cylinder, constructed integrally in the tensioner blade. The two-part connecting link includes an eccentric cam; and the cam can be subjected to the action of tension force by use of the second tensioning device.
Advantageous embodiments and further developments are described and claimed herein.
It is very advantageous if, in a belt assembly according to the invention, the first part of the two-part hinge mechanism is connected to the first tensioner blade; and the second part of the two-part hinge mechanism is connected to the second tensioner blade. The first part of the two-part hinge mechanism exhibits a longer length than the second part; and the hinge point lies outside the area, enclosed by the belt, so that the second tensioning device, required for applying tension force to the hinge point, can lie outside the area, enclosed by the belt. Furthermore, it is deemed to be advantageous, if in a belt assembly with a second tensioner blade, which can be swivelled about a pivotal point, which is stationary on the internal combustion engine, the second tensioning device includes a piston, which is guided in a cylinder, constructed integrally in the second tensioner blade. The axis of the piston goes at least approximately through the pivotal point of the second tensioner blade. In this way, the second tensioning device can support itself in essence on the internal combustion engine side in that the force flows through the pivotal point to the internal combustion engine. According to a preferred embodiment of the invention, the hinge point of the two-part hinge mechanism includes a roll or ball in the contact area to the piston in order to minimize the friction between the hinge point and the piston of the second tensioning device and to avoid forces transversely to the axis of the piston.
As a result of an especially advantageous embodiment of a belt assembly according to the invention, both ends of the piston are guided in the tensioner blade; and the connecting link is connected to the free central area of the piston. Since the piston is subjected to a load transversely to the axis of the piston, the result is a guide that is especially reliable and stressable. In a belt assembly with a second tensioner blade, which can be swivelled about a pivotal point that is stationary on the internal combustion engine, the axis of the piston of the second tensioning device goes advantageously at least approximately through the pivotal point of the second tensioner blade and encloses with the axis of the connecting link an angle α>90 deg.
Especially preferred is a design of a belt assembly according to the invention, in which the cam exhibits a first curved surface and rests with its curved surface against a corresponding surface of the second tensioner blade. The cam exhibits expediently a second curved surface, which forms the contact area in relation to the second tensioning device. In a belt assembly with a second tensioner blade, which can be swivelled about a pivotal point, which is stationary on the internal combustion engine, it is advantageous if the axis of the piston of the second tensioning device goes at least approximately through the pivotal point of the second tensioner blade.
Embodiments of the invention that are to be especially preferred are explained in detail below with reference to the figures. In this respect the figures are shown in the form of a schematic and as examples of the embodiments.